TOPSwitch-GX device dissipaton
Posted by: brucethompson
on
The Design Results portion of PIExpert does not seem to have the power dissipation of the TOPSwitch device expected. There is dissipation for the clamp circuit and the transformer but nothing on the device itself. How can I determine the size of my heatsink without that? There is insufficient information on the power MOSFET to calculate the switching losses myself. I need one or the other: EITHER device dissipation results from PIExpert OR more detailed info on the switching characteristics of the MOSFET so I can calculate the switching losses myself.
Thank you.
There have been several requests to add loss allocation for the power MOSFET. The challange on our part is that particularly the switching losses are a function of external capacitances in the circuit (especially the transformer capacitance)
The following is one (approximate) way to calculate/estimate switching losses.
Conduction loss - This is quite straightforward and can be calculated using IRMS^2 * RDSon.
RDSon is available for each device in the corresponding device datasheet
Switching loss - On a purely theoretical level you can assume that switchnig time is approximately 100 ns. Now you can estimate switching losses by integrating the instantaneous power over 1 second.